(i) Field of the Invention
The present invention relates to a stretched article having a pearly gloss which mainly comprises a polypropylene resin, and a process for producing the stretched article. More specifically, the present invention relates to a stretched article having many fine voids therein and a pearly gloss which can be obtained by adding a specific polyethylene and a specific petroleum hydrocarbon resin having a high softening point to a crystalline polypropylene to form a composition, and then molding the composition, and stretching an obtained molded article and it also relates to a process for producing the same.
(ii) Description of the Related Art
In general, stretched articles having a pearly gloss are used, for example, as usual wrapping materials, decoration materials, synthetic papers, copy papers and the like, in the form of uniaxially and biaxially stretched films, and as packing materials and yarns in the form of tapes, ribbons and filaments.
Conventional and known techniques for providing the molded articles with a pearly gloss are (1) a process comprising the step of adding a glossy material such as a white pigment, an extender pigment or a pearl essence, (2) a process comprising the step of adding a foaming agent at the time of molding to form many foams in the molded articles, (3) a process comprising the step of adding a large amount of an inorganic filler to a crystalline polypropylene, followed by molding and stretching, to form voids in the molded article, as described in Japanese Patent Publication No. 63-24532 and Japanese Patent Application Laid-open No. 63-117043, and (4) a process comprising the step of dispersing a high-melting polymer such as a nylon or a saturated polyester such as polyethylene terephthalate in a crystalline polypropylene (Japanese Patent Application Laid-open No. 61-157547 and U.S. Pat. No. 4,377,616).
However, these techniques have the following drawbacks: In the above-mentioned process (1), different kinds of pigments must be distinctively used to obtain an opaque state and a pearly appearance, and the pearl essence is very expensive. In addition, a particular mixing manner and device for dispersing the pigments are required. The above-mentioned process (2) requires particular molding conditions and the proper selection of the foaming agent in compliance with a use purpose, and in case that a thin film is desired, there is the disadvantage that formation of uniform fine foams is difficult. In the process (3), it is easy to obtain the opaque state by adding a large amount of the inorganic filler, but fluidity at the time of extrusion noticeably deteriorates and a screen pack is clogged. In addition, many troubles are caused in the course of production and, for example, foaming by absorbed moisture and poor dispersion tend to occur owing to the inorganic filler, and a long time is taken to exchange a resin. Articles obtained by process (3) have a poor luster, coarse surfaces, a bad pearly gloss and insufficient impact resistance.
With regard to process (4), nylon, and saturated polyester, such as polyethylene terephthalate or polybutylene terephthalate and the like, are poor in compatibility with crystalline polypropylene. Since nylon and the like are noticeably different from the polypropylene in flow behavior (melting viscosity and the like), uniform dispersion is difficult and a raw fabric is liable to become nonuniform and easily break in a stretching treatment, which means that productivity is poor. Stretched articles are opaque, but there is the problem that the dull articles having a low gloss are only obtained.
The present inventors have conducted various research to obtain opaque stretched articles having a pearly gloss, and as a result, it has been found that the opaque lightweight articles having an excellent pearly gloss and good gas barrier properties can be easily obtained in high productivity by the use of a composition which can be prepared by adding a specific amount of a specific cyclopentadiene petroleum resin to a blend of a polypropylene and a specific polyethylene, and the present invention has been achieved on the basis of this knowledge.